The present application is based on and claims the benefit of U.S. Provisional Application Serial No. 60/178,091, filed Jan. 26, 2000, entitled xe2x80x9cFULLY SUBMERSIBLE IMMERSION HEATER.xe2x80x9d
The present invention relates to the field of immersion heaters. More particularly, the present invention relates to a fully submersible immersion heater having reduced dimensions that is used primarily, but not exclusively, for heating and maintaining the water temperature of an aquarium.
Immersion heaters are known for various purposes, including heating and maintaining the temperature of water in aquariums. As shown in FIG. 1, a typical immersion heater 10 is made up of a heating element 12, a thermostat 14, a power supply cable 16, a waterproof housing 18, an end cap 20, and a temperature control 22. The heating element 12, which is usually a thermal resistance, is electrically connected by one or more wires 13 to the thermostat 14. The thermostat 14, which is typically a thermostatic bimetal camber, is used to regulate the heat output of the heating element 12. The thermostat 14 is in turn electrically connected to the supply cable 16, which supplies power to the heating element 12. The heating element 12, the wires 13, the thermostat 14 and a portion of the supply cable 16 are placed inside the waterproof housing 18, which has an opening (not shown) at one end. The waterproof housing 18 usually comprises a glass tube. The opening in the waterproof housing 18 is sealed with the end cap 20, which is typically made from a rubber material. The end cap 20 has a first conduit 38 (shown in FIG. 4A) and a second conduit 40 (shown in FIG. 4A) that both extend through the end cap 20. The supply cable 16 passes through the first conduit 38 in the end cap 20, allowing the supply cable 16 to be electrically connected to an external power source (not shown). The temperature control 22, typically a knob, dial or button, is seated adjacent to the second conduit 40 in the end cap 20. The temperature control 22 is usually mechanically connected, by a plastic or metallic shaft 24 that passes through the second conduit 40 in the end cap 20, to the thermostat 14. The temperature control 22 allows a user to select or adjust the temperature the immersion heater 10 should maintain. For example, when the user turns or presses the temperature control 22, the shaft 24 respectively rotates or moves vertically to modify the thermostat 14. It will be understood by those of skill in the art that the temperature control 22 could alternatively be electrically connected to the thermostat 14, by replacing the shaft 24 with an electrical cable (not shown).
There are two general designs of conventional immersion heaters for use in heating and maintaining the temperature of water in aquariums. The first such design is illustrated in FIG. 2, in which like numerals are used to indicate like elements without a repeat of the description of the like elements for purposes of brevity. In this design, the upper part of the immersion heater 10 is not watertight because there is no watertight seal between the supply cable 16 and the first conduit 38 in the end cap 22 through which the supply cable 16 passes. The supply cable 16 is usually an SPT1 or SPT2 type cable, because such cables are pliable and relatively thin in cross-section. Even though this design is somewhat resistant to water splashes onto the top of the end cap 22, if the end cap 22 were submerged, water would seep through the first conduit 38 in the end cap 22 and inside the waterproof housing 18. This would create an obvious danger of electrocution to both the fish in the aquarium and the owner, who often has to place his hands in the aquarium water. To obviate this danger, the upper part of the immersion heater 10 is held above the maximum water level 28 of an aquarium 30 by a support 26. This design is disadvantageous in that the immersion heater 10 is only partially submersible and it is not aesthetically pleasing. This design also poses a safety risk in that the support 26 is rarely 100% dependable and it is therefore possible that the end cap 20 may touch the aquarium water.
The second conventional design is illustrated in FIG. 3, in which like numerals are again used to indicate like elements without a repeat of the description of the like elements for purposes of brevity. The immersion heater 10 of FIG. 3 is fully submersible. The supply cable 16 is a relatively large diameter, water-resistant cable having a circular cross section, such as an ST or SJT type cable. Those of skill in the art will appreciate that the circular cross section of the supply cable 16 allows a reliable watertight seal to be achieved between the supply cable 16 and the first conduit 38 in the end cap 20. A watertight seal is also formed between the shaft 24 attached to the temperature control 22 and the second conduit 40 of the end cap 20 in a manner well understood by those of ordinary skill in the art. For example, as shown in FIG. 4B, one or more raised sealing rings 41 can be formed on the interior surface of the second conduit 40. Then, when the shaft 24, which has a diameter that is approximately the same as the diameter of the second conduit 40, is inserted into and through the second conduit 40, an interference fit is formed between the shaft 24 and each of the sealing rings 41 creating a reliable watertight seal.
Even though the immersion heater 10 of FIG. 3 is fully submersible, the design is disadvantageous because the large diameter of the supply cable 16 requires a large end cap and thus a large diameter glass tube to be used as the waterproof housing 18. Such a design is not practical or aesthetically pleasing. Consumers of this type of product like immersion heaters to be discreet in the aquarium. Thus, the waterproof housing 18 should be as small as possible and also the supply cable 16 should be unobtrusive. Neither of these requirements is met by the design of FIG. 3. This design is also disadvantageous because large cables such as the ST or SJT type cables used for the supply cable 16 are rigid and hard to manipulate. For example, a water-resistant ST or SJT type cable can only be bent to produce a curve with a radius of approximately two centimeters. By contrast, a water-resistant SPT1 or SPT2 type cable can be bent to produce a curve with a radius of only three millimeters. The immersion heater 10 of this design is therefore difficult to position or move in an aquarium.
There is a need in the art for an immersion heater, and particularly those for heating and maintaining the temperature of water in aquariums, that is completely submersible but also has reduced dimensions and is thus practical and aesthetically pleasing to consumers. There is also a need for a completely submersible immersion heater that uses a thin, flexible supply cable that is both unobtrusive and easy to manipulate.
Briefly stated, the present invention provides an immersion heater. The immersion heater includes a waterproof housing, an electric heating element, a thermostat, an end cap, a temperature control, a flexible, water-resistant power cable and a sheath. The waterproof housing has an opening at one end. The electric heating element is placed inside of the housing and generates a heat output. The thermostat is placed inside of the housing and is electrically connected to the heating element for regulating the heat output of the heating element. The end cap sealingly engages the opening in the housing to form a watertight seal between the end cap and the opening in the housing. The end cap has a first conduit and a second conduit that extend through the end cap from a first surface of the end cap outside of the housing to a second surface of the end cap inside of the housing. The temperature control is seated adjacent to the second conduit and controls the thermostat. The temperature control is operatively connected to the thermostat by a shaft extending through the second conduit. The shaft sealingly engages the second conduit to form a watertight seal between the shaft and the second conduit. The power cable, which has an outer surface, extends from outside of the housing through the first conduit and is electrically connected to the thermostat inside of the housing. The power cable supplies electrical power to the heating element. The sheath is molded onto the power cable and has an outer surface that is shaped to be complementarily received by the first conduit. The sheath forms a watertight seal with the outer surface of the supply cable and sealingly engages the first conduit to form a watertight seal between the sheath and the first conduit.
In another embodiment, the present invention provides an immersion heater. The immersion heater includes a waterproof housing, an electric heating element, a thermostat, a flexible, water-resistant power cable, an end cap and a temperature control. The waterproof housing has an opening at one end. The electric heating element is placed inside of the housing and generates a heat output. The thermostat is placed inside of the housing and is electrically connected to the heating element for regulating the heat output of the heating element. The power cable, which has an outer surface, extends from outside of the housing and is electrically connected to the thermostat inside of the housing. The power cable supplies electrical power to the heating element. The end cap is molded onto the power cable and sealingly engaging the opening in the housing to form a watertight seal between the end cap and the opening in the housing. The end cap forms a watertight seal with the outer surface of the supply cable. The end cap has a conduit that extends through the end cap from a first surface of the end cap outside of the housing to a second surface of the end cap inside of the housing. The temperature control is seated adjacent to the conduit and controls the thermostat. The temperature control is operatively connected to the thermostat by a shaft extending through the conduit. The shaft sealingly engages the conduit to form a watertight seal between the shaft and the conduit.
In yet another embodiment, the present invention provides a fully submersible immersion heater having reduced dimensions for heating and maintaining the water temperature of an aquarium. The immersion heater includes a glass tube, an electric heating element, a thermostat, an end cap, a temperature control, a flexible, water-resistant power cable and a sheath. The tube has an opening at one end. The electric heating element is placed inside of the tube and generates a heat output. The thermostat is placed inside of the tube and is electrically connected to the heating element for regulating the heat output of the heating element. The end cap sealingly engages the opening in the tube to form a watertight seal between the end cap and the opening in the tube. The end cap has a first conduit and a second conduit that extend through the end cap from a first surface of the end cap outside of the tube to a second surface of the end cap inside of the tube. The temperature control is seated adjacent to the second conduit and controls the thermostat. The temperature control is operatively connected to the thermostat by a shaft extending through the second conduit. The shaft sealingly engages the second conduit to form a watertight seal between the shaft and the second conduit. The power cable, which has an outer surface, extends from outside of the tube through the first conduit and is electrically connected to the thermostat inside of the tube. The power cable supplies electrical power to the heating element. The sheath is molded onto the power cable and has an outer surface that is shaped to be complementarily received by the first conduit. The sheath forms a watertight seal with the outer surface of the supply cable and sealingly engages the first conduit to form a watertight seal between the sheath and the first conduit.